A) Evaporative Emission Systems.
Emission regulations prevent release of gasoline vapors to the atmosphere. To meet such regulations, vehicles are equipped with closed evaporative emission control systems which trap vapors that evaporate from the gasoline in the fuel tank in evaporative canisters containing fuel vapor absorbing substances such as charcoal. Emission regulations currently require that the evaporative canisters and the evaporative emission control system pass not only a pressure maintenance test but also a purge flow test which uses engine vacuum to draw fuel vapors from the tank and those stored in the evaporative canister into the engine for combustion.
It has long been known that emitting fuel vapors from the evaporative canisters into the intake manifold adversely affects the air/fuel ratio present in the combustion chambers of the internal combustion engine. The rich mixture produces excessive emissions and adversely affects driveability and/or engine operation. Accordingly, adjustments to the air/fuel mixture, such as disclosed in U.S. Pat. No. 4,003,358 to Tatsutomi et al., issued Jan. 18, 1977, have been made to account for the fuel vapors admitted to the engine from the evaporative canisters. Not surprisingly, as emission regulations have become more stringent, the controls regulating the flow of the fuel vapors to the engine have become more sophisticated. Thus, in U.S. Pat. No. 5,647,332 to Hyodo et al., issued Jul. 15, 1997, the engine control unit judges the operating condition of the vehicle and controls the opening of an atmospheric cannister control valve to control the mass flow of the vapors emitted from the canisters in accordance with the operating condition of the engine. See also U.S. Pat. No. 5,806,500 to Fargo et al., issued Sep. 15, 1998 in which a plurality of canisters connected in series with a by-pass air purge actuated by the engine control module also controls the fuel delivery to the fuel injectors to insure driveability and emission compliance. See also U.S. Pat. No. 5,816,223 to Rummage et al., issued Feb. 16, 1993, which uses pressure transducers and time rate of change to monitor air/vapor flow to the intake manifold vis-a-vis look-up tables and the like to assure combustion stability and prevent engine roughness or stalling.
In general summary, evaporative canister systems use a pressure regulated air purge to control admission of fuel vapors to the engine through any number of control techniques to maintain the air/fuel ratio at or near stoichiometric during normal engine operation. However, the prior art systems cannot account for the change in hydrocarbon concentration of the fuel vapors such as the change in concentration which occurs when and as the fuel vapors are being exhausted from the canisters. While current evaporative control techniques may be acceptable with engines using standard grades of gasoline and current emission standards, conventional systems may not be acceptable under stricter emission regulations which may be proposed in the future and which will require more accurate fueling control. The prior art does recognize that existing evaporative control system techniques are not acceptable when different types of fuel are used in the vehicle. See, for example, evaporative system control changes should the vehicle be subject to fuels containing alcohol as set forth in U.S. Pat. Nos. 4,945,885 to Gonze et al., issued Aug. 7, 1990; 5,111,796 to Ogita, issued May 12, 1992; and, 5,231,969 to Suga, issued Aug. 3, 1993.
B) Cold-Start.
Proposed emission standards require that a regulated drive cycle such as an FTP (Federal Test Procedure) or its European equivalent (an MVG), include a "cold-start" requirement. "Cold-start" conventionally means a condition where the engine and catalytic converter are at temperatures not greater than about 50.degree. C. at the time the engine is started. When the engine is started from a cold condition, the catalytic converter is not catalytically active. In fact, a substantial amount of the emissions produced by the vehicle over a regulated drive cycle are attributed to the emissions produced at cold-start and during engine warm-up following a cold-start. (Warm-up of the engine occurs when the catalytic converter becomes substantially catalytically active, i.e., a condition conventionally defined to mean that 50% of the combustible emissions (CO, HC, H.sub.2, NO.sub.x) are converted by the catalytic converter to N.sub.2, CO.sub.2 and H.sub.2 and often times is referred to as "light-off" of the catalytic converter.) Further, emission sensors, typically EGO (exhaust gas oxygen) sensors, cannot provide a feedback signal at cold-start so the fueling control is open loop and not closed loop.
Emission control at cold-start and during warm-up has generated a separate body of prior art directed to resolving this problem such as the development of light-off catalysts, NO.sub.x traps, etc.
Most significant, however, is the fact that it is well understood in the prior art that pre-vaporization of the fuel materially reduces the presence of regulated emissions emitted by the engine during cold-start and warm-up. This can be documented from any number of sources such as SAE papers No. 860246, dated Feb. 24-28, 1986, entitled "An Evaluation of Local Heating as a Means of Fuel Evaporation For Gasoline Engines"; 930710, dated Mar. 1-5, 1993, entitled "Cold Start Performance of an Automotive Engine Using Prevaporized Gasoline"; and 961957, dated Oct. 14-17, 1996, entitled "Effect of Fuel Preparation on Cold-Start Hydrocarbon Emissions from a Spark-Ignited Engine", all of which are hereby incorporated herein by reference.
The prior art has adopted a number of arrangements utilizing pre-vaporized fuel for reducing emissions produced during cold-start and warm-up of an internal combustion engine. In U.S. Pat. No. 5,529,035 to Hunt et al., issued Jun. 25, 1996, a heated cold-start fuel injector introduces vaporized fuel to the fuel rail of the engine. In U.S. Pat. No. 5,694,906 to Lange et al., issued Dec. 9, 1997, an unheated fuel vaporizer injector is used for cold-start which converts to regular fuel injection operation when the engine reaches normal operating conditions. In U.S. Pat. No. 5,482,023 to Hunt et al., issued Jan. 9, 1996, a heated cold-start injector along with fuel vapors from the evaporator canister are used for cold-start. In U.S. Pat. No. 5,850,822 to Romann et al., issued Dec. 22, 1998, two fuel injector valves are utilized with the cold-start heated injector fueling the engine through one intake valve during cold-start and warmup phases, and the conventional injector fueling the engine through the "normal" intake valve at normal operating engine temperatures. In U.S. Pat. No. 5,850,821 to Curtis, issued Dec. 22, 1998, a non-heated cold-start injector is utilized and the observation is made that it is not known what vaporization is achieved. Curtis then measures the temperature or calculates the temperature to determine an estimated fuel vaporization. All of these systems assume that a fuel vaporization level is achieved at a given temperature and that the vaporization will, in turn, achieve certain expected results when the vapors are combusted in the combustion chamber of the engine. More particularly, given the relatively narrow composition range of detergent grade gasoline, a fuel vaporizer will produce known hydrocarbon gas compositions at elevated temperature such that timing and air to fuel ratios can be set to assure desired combustion. However, different fuels can be used and even detergent grade gasolines have different octane ratings. What is actually needed, or will be needed to meet future emission regulations, is a direct measurement of the gas phase fuel concentration or air to fuel ratio of the mixture ported to the combustion chambers of the engine.
C) Infrared Sensors.
Infrared sensors can measure hydrocarbon concentrations in a gas but if the hydrocarbon concentration produces an explosive mixture, the infrared sensors must be equipped with a flame arrester to prevent auto ignition of the gas from the infrared source. The flame arrester severely limits the sample flow rate of the gas to be measured through the sensor resulting in a slow response time. U.S. Pat. No. 4,323,777 to Baskins et al., issued Apr. 6, 1982 (incorporated herein by reference), illustrates the ability of infrared sensor to detect the presence of hydrocarbon vapors in a gas sample, but at relatively low hydrocarbon level concentrations such that the gas being sensed is not flammable, i.e., at concentrations below the lower explosive limit of the gases being sensed. The Baskins device is primarily concerned with toxicity. More pertinent is U.S. Pat. No. 5,608,219 to Aucremanne, issued Mar. 4, 1997 (incorporated herein by reference), uses a large sized infrared source to maintain the black body temperature below the auto ignition temperature of the gaseous mixture thus obviating the need for a flame arrester or similar devices. However, the sensor response as shown in the graphs of the '219 patent is slow, and is believed too slow to permit use in the fuel controls of an internal combustion engine.
D) Infrared Sensors in the Automotive Field.
In U.S. Pat. No. 5,401,967 to Stedman et al., issued Mar. 28, 1995, an infrared sensor is used to determine the presence and concentration of regulated emissions in the exhaust gas of an internal combustion engine. The emissions in the exhaust gas are not in sufficient concentration to present a flammable or explosive mixture. In U.S. Pat. No. 5,782,275 to Hartsell, Jr. et al., issued Jul. 21, 1998, an infrared sensor is used in a fuel dispensing system (gas station) to determine if the vehicle being fueled is equipped with a vapor recovery system. In U.S. Pat. No. 5,225,679 to Clark et al., issued Jul. 6, 1993, an infrared sensor is used to determine the octane content of gas supplied at the service station pump to a vehicle. Somewhat similar is U.S. Pat. No. 5,262,645 to Lambert et al., issued Nov. 16, 1993, which utilizes an infrared sensor to detect the alcohol content of an alcohol/gasoline mixture used as the fuel for a vehicle. In the latter three references, the black body heat emitted by the infrared source will not exceed the flammability index of the liquid fuel being measured. Clark et al. and Lambert et al. are concerned with measurements of liquids, which while highly flammable, have a higher auto ignition temperature than if the liquid was in a combustible gas/air form.